Crumbly grout is usually from using unsanded grout in too wide of a joint. In general, unsanded should only be used in joints less than 1/8" wide. For joints 1/8" or wider, sanded grout should be used. I have seen grout fall out where it was mixed with too much water, and when placed it was not really worked into the grout joints. So the joints were not completely full, and when the excess water evaporated, it left behind a sponge-like grout matrix. It would simply chunk out. Changes in plane, like a wall to a tub, are usually caulked. That's because dissimilar materials can move independently. Rigid grout would crack. Flexible caulk can flex. To make the caulk less obtrusive, there are color- and texture-matching caulks out there. Example, you use sage green sanded grout from "X" company, they might also have a sage green sanded caulk to match that grout. It might not be a perfect match, but it's better than picking any caulk off the shelf. Gas seeping through grout and staining it? Ehhh...I'll pass on that. I've heard a lot of strange ideas while mediating the blame game in the past, but I don't ever recall that one being brought up. If it was a mud bed, moisture evaporation can carry dissolved minerals from the mud pan up through the grout, and when the water hits free air and evaporates, it can leave mineral stains or mineral grit behind. If there is a water leak at this window, your stains could be a variation of that. If it's an orange stain, it could indeed be rust. It could be a nail head used to fasten the cement backer board that is rusting, etc, and it's wicking through the grout. Or something else. Iron in the water, etc.

seattlemamadrama ~Well my Wasauna story ended badly. The first tub was drained the wrong way for me. I shipped it back at their expense and received my replacement last week. The crate was in horrible condition, held together by plastic wrap about 2 times around it. The person who sent it to me must have received my tub and we just traded. I sent him one in perfect condition never removed from the crate. The tub he sent me was dirty, removed from the crate and damaged with scratches. I refused the delivery and call Alex for a refund. He tried to give me 300.00 off and get a new one sent to me but I just took my refund. I have not seen the credit on my card as yet, it has been 4 days. I would say stay away from them. I am in the process of looking for something else now. Good luck to you! Mariofo

Water buildup behind the tile on a properly built unit is marginal. What you get is water vapor for the most part, which generally gravitates to the morter and evaporates on a surface applied build, or on the cement board in a traditional, plastic-over-the-studs application. 100% Silicone should be used at any change-of-plane because of the small, perhaps even microscopic movement that is inevitable there. With a solid, cast tub and mud walls, you could probably "get by" with grouting those joints. With the usual, flimsier tubs, I like to fill with water, thereby "loading" the tub and then caulking in that position so that stress is minimal on the caulk under use and heavy weight.

Bleach apparently won't kill mold (read this somewhere while researching/cleaning). When we had a recurrence of tile/caulk darkening in one small spot at the base of the MB tub surround, I scraped out the caulk in that spot, and then hit the space with vinegar, hydrogen peroxide with and without baking soda, not necessarily in that order. After cleaning it all off/out, I let it air dry really well, and then re-caulked, using the same siliconized latex caulk (that matched the grout). If it does happen again, we'll scrape out the caulk, and use 100% silicone caulk. We also wipe down the walls with a microfiber cloth after showering, especially where the tile meets the tub. I couldn't find a squeegee that I liked, and I think the cloth does a better job wiping away water droplets (which, with our moderately hard water, leaves ugly water spots on our shiny white tile), and does a better job sopping up the pool of water that would otherwise sit along the edge of the tub, at the base of the tile and caulk.